Buck converters are widely used for DC-DC conversion, and preferably have high efficiency. To achieve high efficiency, the high-side and low-side power transistors of a buck converter output stage must be switched very fast and use as little margin (i.e. dead time) as possible. However, when switching very quickly, a voltage is induced on the gate of at least one of the power transistors. Such an induced gate voltage leads to a turn-on of the device, cross-conduction, and very high losses unless the dead time is set long enough to avoid these conditions.
Power HEMTs (high-electron-mobility transistors) theoretically provide significant power density, on-state resistance, switching frequency, and efficiency benefits over silicon MOSFETs in DC-DC converters, but pose new challenges for designers. For example, buck converters are typically packaged with the power transistors of the output stage disposed in one or more dies (chips) and the driver for the output stage on a separate die. With such an arrangement, the inductance between the driver and the gate of the output stage power transistors is so high that the gate voltage cannot be perfectly controlled due to the dynamic voltage drop over the series parasitic resistance and inductance. This, in turn, causes voltage spikes at the gate of the power transistors unless the dead time is increased, which, in turn, reduces efficiency. If left unmitigated, such voltage spikes preclude the use of HEMTs in power converters because conventional HEMTs are much more susceptible to gate voltage spikes than silicon MOSFETs.